Unable to separate by loose parts
Well it's been about a week and with no real help here, I tinkered and finally came up with a solution.  Deleting the connecting vertices between the side panels and the arm.  There were two cylinders I had extruded from the arm through the side panels, which caused the problem.

 

You can test yourself by using the sample file I uploaded here at moonboots  request


tab into object mode
select object 
tab into edit mode
select all faces
click P and select "by loose parts"
tab back to object mode
deselect all
select long arm and notice side panels are still connected
tab into edit mode
using faces select mode, press Alt and LMB to select all faces of first cylinder in the center of the arm.
press Shift-Alt-LMB and select all center faces of 2nd cylinder
press delete button and select vertices
tab into object mode and deselect all
verify side panels have been separated from arm by selecting each item


I now just had a few missing faces that needed to be filled in, but I preserved the location and size of all the pieces so they would fit in the model.  Also I was able to finish the editing I needed to do, to prepare my model for 3D printing.  You can verify how the assembly fits into the total model by clicking on the eye icon next to "frame" in the outliner.